Objective lens driving device and optical pickup device employing the objective lens driving device

ABSTRACT

The present invention is relative with an objective lens driving device used in an optical pickup device, and includes a stationary unit, a lens bobbin provided with an objective lens, at least one magnet provided on one of the lens bobbin and the stationary unit, a coil unit provided on the other of the lens bobbin and the stationary unit for causing movement of the lens bobbin in a direction parallel to the optical axis of the objective lens and in a planar direction perpendicular to the optical axis of the objective lens, and an elastic supporting unit of a stainless material, provided between a stationary unit and the lens bobbin. The elastic supporting unit supports the lens bobbin for movement in a direction parallel to the optical axis of the objective lens and in a planar direction perpendicular to the optical axis of the objective lens.

This application is a 371 of PCT/JP02/01867 Feb. 28, 2002.

TECHNICAL FIELD

This invention relates to an optical pickup device, used for writinginformation signals on an optical recording medium, such as an opticaldisc, and for reading out the information signals, recorded on thisrecording mediwn, and to an objective lens driving device which may beusefully applied to this optical pickup device.

BACKGROUND ART

An optical pickup device is routinely used for writing informationsignals on an optical recording medium, such as an optical disc, and forreading out the information signals recorded on this recording medium.This type of the optical pickup device includes a main body unit,provided with a light source, such as a semiconductor laser, and with alight receiving element, such as a photodiode, an objective lens, onwhich falls a light beam radiated from the light source, and a drivingmechanism for deflecting this objective lens in a preset direction,which will be explained subsequently.

This objective lens driving mechanism supports an objective lens,adapted for converging the light beam, radiated from a light source,along a direction of the optical axis of the objective lens, that is inthe focusing direction, and along a direction perpendicular to theoptical axis, that is in the tracking direction, while causing theobjective lens to be deflected by an electromagnetic actuator in thefocusing and tracking directions. The objective lens driving mechanismcauses movement of this objective lens to be moved along the directionof the optical axis of the objective lens and along the directionperpendicular to the optical axis to cause a light spot formed by thisobjective lens on a signal recording surface of the optical recordingmedium to follow a recording track on the signal recording surface ofthe optical recording medium. That is, the objective lens drivingmechanism causes the objective lens to be moved along the direction ofthe optical axis of the objective lens, that is in the focusingdirection, to execute focusing control of converging the light beamradiated from the light source on the signal recording surface. Theobjective lens driving mechanism also causes the objective lens to bemoved in the focusing direction along the optical axis of the objectivelens, and in the tracking direction, that is in a directionperpendicular to the tangential line of the recording track, to cause alight converging point of the light beam radiated from the light sourceto follow the recording track, by way of performing tracking adjustment.

The objective lens driving mechanism includes a stationary unit, mountedon the main body unit, a lens bobbin, carrying the objective lens, and asupporting member interconnecting the stationary unit and the lensbobbin. The supporting unit is made up by four flexible fine linearmembers and supports the lens bobbin for movement along the directionparallel to the optical axis and along the direction perpendicular tothe optical axis with respect to the stationary unit. That is, each ofthe linear members making up the supporting unit has its one end mountedon the stationary unit, while having its other end mounted on the lensbobbin.

The stationary unit is provided with a magnetic circuit unit comprisedof a magnet and a yoke. On the lens bobbin are mounted a driving coilfor focusing and another driving coil for tracking, both mounted in amagnetic field generated by a magnet constituting the magnetic circuitunit. In this objective lens driving mechanism, when the current issupplied to the driving coil for focusing, the driving coil for focusingis moved, along with the lens bobbin, along the direction of the opticalaxis of the objective lens, together with the lens bobbin, under theinteraction with the magnetic field generated by the magnetic circuitunit. When the current is supplied to the driving coil for tracking, thedriving coil for tracking is moved, along with the lens bobbin, in thedirection perpendicular to the optical axis of the objective lens, alongwith the lens bobbin, under the interaction with the magnetic fieldgenerated by the magnetic circuit unit. By this interaction between therespective driving coils and the magnetic circuit unit, focusing controland tracking control are executed so that the light spot of the lightbeam radiated from the light source and converged on the signalrecording surface by the objective lens will follow up with verticalmovement of the signal recording surface and with the recording track.

In this objective lens driving mechanism, current supply to therespective driving coils is via the respective linear members formingthe supporting unit. Consequently, these linear members are desirablyformed of a material which is low in electrical resistance and whichdoes not produce resonance in the frequency range used, for example,such a material as beryllium copper. Meanwhile, these linear members areof a thickness of the order of 80 μm, a width up to 80 to 90 μm and alength of the order of 15 to 20 mm.

In the above-described objective lens driving device, since the fourlinear members forming the supporting unit are used as feeder lines forthe driving coil for focusing and for the driving coil for tracking, andhence need to be electrically independent of and electrically insulatedfrom each other. Therefore, the linear members forming the supportingunit must be formed as respectively separate members.

These linear members were difficult to form to high precision in amanner free from distortion or flexure. These linear members are formedby first punching a plate member, and by providing a unit comprised ofplural linear members 101, 101 lying within a frame-shaped frame 102,with the ends of the linear members being secured to the inner sideedges of the frame 102, as shown in FIG. 1. The linear members 101, 101then are severed from the frame 102. However, when severed from theframe 102, the linear members 101 tend to be distorted or flexed.

It may be contemplated to interconnect both ends of the two linearmembers 101, 101, neighboring to the objective lens driving mechanism,by synthetic resin components 103, 103, by insert molding, as the plurallinear members 101, 101 are supported by the frame 102, therebysuppressing torsion or flexure of the linear members 101, 101. In thiscase, both ends of the two linear members 101, 101 are severed from theframe 102, as both ends of the linear members 101, 101 remain connectedto the synthetic resin components 103, 103. The resulting unit is usedin this state as the objective lens driving device. If the linearmembers 101, 101 are connected by the synthetic resin components 103,103 to the frame as described above, the resulting unit becomes thickerthan the liner members per se. The unit carrying the linear members 101,101 thus connected is locally different in thickness, so that, if aplural number of such units are stacked directly together, the linearmembers 101, 101 tend to be deformed. For transporting the units,carrying the linear members 101, 101, thus connected, in a state ofpreventing the linear members 101 from becoming deformed, dedicatedpacking materials need to be used. If a large number of the units,carrying the linear members 101, 101, are to be packaged andtransported, the packages for transport, employing the dedicatedpackaging materials, are bulky in size, to render it impossible toimprove the transport efficiency.

Moreover, beryllium copper, retained to be convenient as a materialforming the above-mentioned linear members, is difficult to procure,while being costly.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide anobjective lens driving device, in which linear members supporting a lensbobbin may readily be formed, the supporting members may be packaged andtransported readily and in which the materials of the supporting memberscan be procured easily and manufactured inexpensively. It is anotherobject of the present invention to provide an optical pickup deviceemploying this objective lens driving device.

For accomplishing the above object, the present invention provides anobjective lens driving device including a lens bobbin provided with anobjective lens, at least one magnet provided on the lens bobbin, a coilunit for causing movement of the lens bobbin along with the magnet in adirection parallel to the optical axis of the objective lens and in aplanar direction perpendicular to the optical axis of the objectivelens, a stationary unit provided with the coil unit, and an elasticsupporting unit of a stainless material, provided between the stationaryunit and the lens bobbin; the elastic supporting unit supporting thelens bobbin for movement in a direction parallel to the optical axis ofthe objective lens and in a planar direction perpendicular to theoptical axis of the objective lens.

The elastic supporting unit includes a plurality of linear supportingmembers each having its one end mounted to the lens bobbin and havingits opposite end to the stationary unit.

The elastic supporting unit includes a first elastic supporting part anda second elastic supporting part, each constructed as two connectingpieces, each of the connecting pieces interconnecting both ends of twoof the plural supporting members so that the two supporting membersextend parallel to each other.

The first and second elastic supporting parts are formed on punching astainless sheet material into a stainless plate member.

The stationary unit includes a plurality of grooves adapted forreceiving the opposite ends of the plural supporting members. In eachgroove, there is provided a damper in contact with the opposite end ofthe associated supporting member.

A substantially rectangular frame-shaped yoke is provided in the lensbobbin, two magnets are provided at a preset distance between two facinginner wall sections of the yoke and wherein the coil unit is providedbetween the magnets.

The present invention also provides an objective lens driving deviceincluding a stationary unit, a lens bobbin provided with an objectivelens, at least one magnet provided on one of the lens bobbin and thestationary unit, a coil unit provided on the other of the lens bobbinand the stationary unit and adapted for supporting the lens bobbin formovement in a direction parallel to the optical axis of the objectivelens and in a planar direction perpendicular to the optical axis of theoptical axis of the objective lens, and an elastic supporting unit of astainless material, provided between the stationary unit and the lensbobbin; the elastic supporting unit supporting the lens bobbin formovement in a direction parallel to the optical axis of the objectivelens and in a planar direction perpendicular to the optical axis of theobjective lens.

The present invention also provides an optical pickup device including alight source, an objective lens driving device, and a photodetector fordetecting the light beam incident thereon via the objective lens. Theobjective lens driving device includes a lens bobbin, provided with anobjective lens for converging a light beam radiated from the lightsource, a stationary unit having an opening for guiding the light beamradiated from the light source to the objective lens, at least onemagnet mounted on one of the lens bobbin and the stationary unit, a coilunit provided on the other of the lens bobbin and the stationary unitand adapted for causing movement of the lens bobbin in a directionparallel to the optical axis of the objective lens and in a planardirection perpendicular to the optical axis of the objective lens, andan elastic supporting unit of a stainless material provided between thestationary unit and the lens bobbin for supporting the lens bobbin formovement in a direction parallel to the optical axis of the objectivelens and in a planar direction perpendicular to the optical axis of theobjective lens.

Other objects, features and advantages of the present invention willbecome more apparent from reading the embodiments of the presentinvention as shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a supporting member used for aconventional objective lens driving device.

FIG. 2 is a perspective view showing an objective lens driving deviceaccording to the present invention.

FIG. 3 is an exploded perspective view showing the objective lensdriving device according to the present invention.

FIG. 4 is a plan view showing the objective lens driving deviceaccording to the present invention.

FIG. 5 is a side view thereof.

FIG. 6 is a front view thereof.

FIG. 7 is a plan view showing the status in the course of manufacturinga supporting member forming the objective lens driving device.

FIG. 8 is a plan view showing the supporting member used in theobjective lens driving device according to the present invention.

FIG. 9 is a longitudinal cross-sectional view showing an optical pickupdevice according to the present invention.

FIG. 10 is a graph showing oscillation characteristics of a movable unitof the objective lens driving device of the present invention in adirection parallel to the optical axis of the objective lens.

FIG. 11 is a graph showing oscillation characteristics of the movableunit in a planar direction perpendicular to the optical axis of theobjective lens.

FIG. 12 is a graph showing oscillation characteristics of a movable unitof a conventional objective lens driving device in a direction parallelto the optical axis of an objective lens.

FIG. 13 is a graph showing oscillation characteristics of the movableunit in a planar direction perpendicular to the optical axis of theobjective lens.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is now explained with reference to an embodimentthereof as applied to an objective lens driving device used forrecording information signals on an optical disc as an optical recordingmedium and for reading out the information signals recorded on therecording medium.

Referring to FIGS. 2 to 4, the objective lens driving device accordingto the present invention includes a base member 1, as a stationary unit,a lens bobbin 3, carrying an objective lens 2, and four supportingmembers 4 a, as an elastic supporting unit, interconnecting thestationary unit and the lens bobbin.

The base member 1 is formed as a unitary member, from a synthetic resinmaterial, as a substantially planar member. On the upper rear surface ofthe base member 1, there are formed upright a supporting plate 5 and apair of supporting pillars 6, 6. Between the supporting plate 5 and thesupporting pillars 6, 6 is mounted a substantially flat mounting plate 7with light press fitting. The mounting plate 7 is mounted in position bybeing introduced into a space between the supporting plate 5 and thesupporting pillars 6, 6. This mounting plate 7 carries a pair ofmounting arms 8, 8 on its both sides, as shown in FIG. 3. The mountingarms 8, 8 are formed as arms protruded on both sides from the mountingplate 7, with the foremost flat parts thereof extending parallel to eachother. At mid portions of the foremost flat parts of the mounting arms8, 8 are formed positioning projections 9.

The supporting members 4 a are formed as fine flexible linear members,and support the lens bobbin 3 for movement in a direction indicated byarrow F and in a direction indicated by arrow T in FIG. 2 with respectto the base member 1. That is, each supporting member 4 a has its oneend and its other end mounted on the base member 1 and on the lensbobbin 3, respectively, as shown in FIGS. 2 to 4. The two supportingmembers 4 a, lying in a direction parallel to the optical axis of theobjective lens 2, are grouped together as a set and have theirrespective ends connected together by connecting pieces 10, 10. Thesesupporting members 4 a are formed as one unitary unit from a stainlessmaterial, as the supporting member 4 a run parallel to each other and tothe optical axis of the objective lens 2, as shown in FIG. 3. That is,the two supporting members 4 a, 4 a and the two connecting pieces 10, 10are punched respectively as one unit from a sheet of a stainlessmaterial and are coupled together in a manner which will be explainedsubsequently.

Each of the connecting pieces 10, 10 is formed at its mid portion with apositioning hole 11. The positioning hole 11 of the connecting piece 10provided at one end is circular, while the positioning hole 11 of theconnecting piece 10 provided at the opposite end is an elliptical holehaving its long axis along the direction parallel to the supportingmembers 4 a. On both sides of the positioning hole 11 of each of theconnecting pieces 10, 10 is formed a pair of bonding holes 12, 12.

Referring to FIG. 3, the positioning projections 9 of the mounting arms8, 8 are inserted into the positioning holes 11 of the connecting pieces10, 10 on one side and an adhesive 13 is applied to the bonding holes12, 12 to secure the connecting pieces 10, 10 to the end faces of themounting arms 8, 8 to secure elastic supporting units 4, 4 to the endfaces of the mounting arms 8, 8. At this time, the supporting members 4a, 4 a, 4 a, 4 a are supported in a cantilevered fashion for extendingin a forward direction formed the mounting arms 8, 8 over the lateralsides of the supporting plate 5, as shown in FIG. 2. The two elasticsupporting units 4, 4 are mounted between the lens bobbin 3 and thesupporting plate 5, on both sides of the objective lens 2, so as to beparallel to each other, as shown in FIG. 2 or 4. With the connectingpieces 10, 10 on one sides of the supporting members 4 a, 4 a mounted tothe mounting arms 8, 8 on both sides, the sum of four supporting members4 a, 4 a are carried by the respective mounting arms 8, 8 for extendingforwards in a cantilevered fashion over the lateral sides of thesupporting plate 5, in a direction parallel to each other, as shown inFIG. 2.

In both lateral sides of the supporting plate 5 are formed upper andlower paired damper holding grooves 14, 14, as shown in FIGS. 2, 3 and5. The elastic supporting units 4, 4 are carried by the mounting arms 8,8 through the damper holding grooves 14, 14 for extending in a forwarddirection, as shown in FIG. 2. In these damper holding grooves 14, 14are charged gelated dampers 15 formed of a silicon-based material. Thesedampers 15 are contacted with rim portions, specifically, one endportions, of the elastic supporting units 4, 4, as shown in FIG. 2. Theresult is that oscillation characteristics of a movable unit, includingthe lens bobbin 3, supported by this elastic supporting units 4, 4, aslater explained, are corrected by the dampers 15.

The lens bobbin 3 is mounted on the connecting pieces 10, 10 lying onthe opposite side of the respective elastic supporting units 4, 4. Thelens bobbin 3, formed of a synthetic resin material, includes anobjective lens mounting hole 16, as a through-hole, as shown in FIG. 3.The lens bobbin 3 includes a yoke 17 formed of a high magneticpermeability material. In this objective lens mounting hole 16 ismounted the objective lens 2, such as an aspheric lens. The yoke 17 isformed as a rectangular frame, as shown in FIGS. 3 and 4, and is unifiedto the lens bobbin 3 by insert molding. In this lens bobbin 3, theobjective lens mounting hole 16 is provided at a mid portion of the lensbobbin 3, while the yoke 17 is positioned forwardly of the objectivelens mounting hole 16 of the lens bobbin 3, as shown in FIGS. 3 and 4.The lens bobbin 3 is provided with a pair of mounting surfaces 18, 18lying on both sides of the yoke 17. These mounting surfaces 18, 18 areplanar and formed so as to be parallel to each other. At mid portions ofthe respective mounting surfaces 18, 18 are formed positioningprotuberances 19, 19.

The elastic supporting units 4, 4 are mounted on the respective mountingsurfaces 18, 18, as shown in FIG. 2, as the positioning protuberances19, 19 provided on the mounting surfaces 18, 18 of the lens bobbin 3 areinserted into the positioning holes 11 of the opposite side connectingpieces 10, 10, and as an adhesive 20 is subsequently coated and chargedinto the bonding holes 12, 12 for bonding the connecting pieces 10, 10and the mounting surfaces 18, 18 to each other with the adhesive 20. Inthis manner, the lens bobbin 3 is supported by the four supportingmembers 4 a, 4 a, 4 a, 4 a. At this time, the objective lens 2 ismounted so that its optical axis will be perpendicular to the uppersurface of the base in member 1. At a mid portion of the base member 1in register with the so mounted objective lens 2, there is bored athrough-hole as an opening through which is transmitted the light beamso as to be incident on the objective lens 2.

The elastic supporting units 4, 4 are formed of stainless material andhence is flexible, so that it is movable in a focusing direction whichis parallel to the optical axis of the objective lens 2, as indicated byarrow F in FIG. 2, and in a planar tracking direction which isperpendicular to the optical axis of the objective lens 2, as indicatedby arrow T in FIG. 2. When the lens bobbin 3 is moved in this manner inthe directions indicated by arrows F or T in FIG. 2, there is no risk ofthe optical axis of the objective lens 2 becoming tumbled or tilted,because the lens bobbin 3 is carried by the four supporting members 4 a.

The lens bobbin 3 is provided with a pair of magnets 21, 21 forming amagnetic circuit unit in cooperation with the yoke 17. The magnets 21,21, forming the magnetic circuit unit, are each formed to a rectangularshape, and are mounted by the inner wall section of the yoke 17, formedto a rectangular frame shape, as described above, in a facingrelationship to each other via a preset gap, as shown in FIG. 3. Thesemagnets 21, 21 are mounted at a mid portion of the forward side innerwall section and at a mid portion of the rear side inner wall section,as shown in FIG. 4. By these magnets 21, 21 and the yoke 17, there isgenerated, at a mid portion within the inside of the yoke 17, that is ina spacing defined between the magnets 21, 21, a magnetic field in whichthe direction of the magnetic flux is along the forward and backwarddirection.

The lens bobbin 3, inclusive of the yoke 17, the objective lens 2mounted on this lens bobbin 3, the connecting pieces 10, 10, lying onthe opposite side of the elastic supporting units 4, 4, the adhesive 20and the magnets 21, 21, mounted on the yoke 17, make up a movable unitin the objective lens driving device.

The base member 1 carries focusing driving coils 22, 22 and trackingdriving coils 23, 23, so that these coils will be located in themagnetic field generated by the magnets 21, 21 forming theabove-mentioned magnetic circuit unit. The focusing driving coils 22, 22are each formed by winding an electrically conductive linear member inthe form of a horizontally elongated ellipse, while the tracking drivingcoils 23, 23 are each formed by winding an electrically conductivelinear member in the form of a longitudinally elongated ellipse. Thesefocusing driving coils 22, 22 and tracking driving coils 23, 23 arecarried at the respective lower sides in driving coil holding grooves 24formed in the upper surface of the base member 1, as shown in FIG. 3.The tracking driving coils 23, 23 are held side-by-side in the holdinggroove 24, while the focusing driving coils 22, 22 are held in theholding groove 24 for sandwiching the tracking driving coils 23, 23 fromthe forward and rear sides, as shown in FIGS. 2 to 4.

The focusing driving coils 22, 22 and the tracking driving coils 23, 23are introduced into the gap defined between the magnets 21, 21 withinthe yoke 17 of the lens bobbin 3, in the form of a rectangular frame, asshown in FIG. 6. The upper horizontal linear portions of the focusingdriving coils 22, 22 and linear vertical portions of the mutuallyadjacent sides of the tracking driving coils 23, 23 intersect each otherat the center within the inside of the yoke 17. The intersectingportions of the focusing driving coils 22, 22 and the tracking drivingcoils 23, 23 are located in a spacing between the magnets 21, 21.

The base member 1 is provided with four terminals 25 held within thebase member 1 and having foremost parts protruded forwards from thefront end thereof, as shown in FIG. 3. These terminals 25 are connectedto one ends of the focusing driving coils 22, 22, to opposite endsthereof, to one ends of the tracking driving coils 23, 23 and to theopposite ends thereof, by outlet lines, not shown. As a result, thefocusing servo signals and tracking servo signals are supplied asdriving signals to the focusing driving coils 22, 22 and trackingdriving coils 23, 23. The outlet lines are connected through the insideof the base member 1 to the respective terminals 25 and to therespective driving coils 22, 22 and 23, 23.

If, in the present objective lens driving device, the focusing servosignals are sent to the focusing driving coils 22, 22, the objectivelens 2 is moved, along with the lens bobbin 3, in the focusing directionparallel to the optical axis of the objective lens 2, as indicated byarrow F in FIG. 6, under the interaction of the magnetic field generatedby the magnets 21, 21 forming the magnetic circuit unit and thatgenerated by the focusing driving coils 22, 22. If, in this objectivelens driving device, the tracking servo signals are sent to the trackingdriving coils 23, 23, the objective lens 2 is moved, along with the lensbobbin 3, in the tracking direction perpendicular to the optical axis ofthe objective lens 2, as indicated by arrow T in FIG. 6, under theinteraction of the magnetic field generated by the magnets 21,21 formingthe magnetic circuit unit and that generated by the tracking drivingcoils 23, 23. This interaction between the respective driving coils 22,23 and the magnetic circuit unit provides for focusing and trackingcontrol in the optical pickup device as will be explained subsequently.

On the base member 1, a semi-cylindrical dust-proofing wall section 28is formed upright as one with the base member 1 for surrounding the lensbobbin 3, outside its movement sphere, as shown in FIGS. 2, 3 and 4.

In the objective lens driving device of the present invention, drivingsignals are supplied to the respective driving coils not from thesupporting members 4 a but from the terminals 25 via outlet lines, asdescribed above. Thus, the supporting members 4 a do not have to beinsulated electrically from one another, but may be used as both endsthereof remain coupled to the connecting pieces 10, 10. Since there isno limitation to the materials making up the supporting members 4 a,insofar as the electrical resistance is concerned, any suitable materialthat is readily available, inexpensive and amenable to working, and thatis not subjected to resonant oscillations in the operating frequencyrange, may be used. The present objective lens driving device usesstainless material (chromium alloys), such as ‘SUS301’ or ‘SUS304’ asprescribed by JIS (Japan Industrial Standard) as such materialsatisfying the above requirements.

In forming the supporting members 4 a from such material, a plate memberof stainless material, about 80 μm in thickness, as a rectangular frame26, is formed on punching. The two supporting members 4 a, 4 a and theconnecting pieces 10, 10 on both ends of the supporting members 4 a, 4 aare connected to the rectangular frame 26 via two straitened portions27, on each of both ends of the frame 26 within the boundaries of therectangular frame 26, as shown in FIG. 7. The positioning holes 11 andthe bonding holes 12, 12 are simultaneously formed on punching. Thestraitened portions 27 of the member shown in FIG. 7 are cut to completeelastic supporting units 4, 4, having supporting members 4 a, both endsof which are interconnected by the connecting pieces 10, 10, as shown inFIG. 8.

The elastic supporting units 4, 4 remain connected at both ends by theconnecting pieces 10, 10, even after disconnection from the frame 26,and hence are not subjected to distortion or flexure. Depending on theprecision of a metal mold, used for punching, high precision machiningmay be achieved as to the pitch between the two supporting members 4 a,4 a or the location of the positioning holes 11.

A large number of the elastic supporting units 4, still remainingconnected to the frames 26, may be stacked for packaging and transport.The elastic supporting units 4, 4, connected to the frame 26, are in theform of a flat sheet with a thickness on the order of 80 μm, are notbulky on being stacked, while being not liable to distortion. Since theeis no necessity of employing dedicated packaging materials, thetransport efficiency may be improved. Meanwhile, the elastic supportingunit 4, used in the present invention, is approximately 80 to 90 μm inwidth and approximately 15 to 20 mm in length.

As for oscillation characteristics of the movable unit of the opticalpickup device, the resonance frequency (f0) in a direction parallel tothe optical axis of the objective lens 2 (FCS) is 29.5 Hz, as shown inFIG. 10, while the resonance frequency (f0) in the planar directionperpendicular to the optical axis of the objective lens 2 is 27.0 Hz, asshown in FIG. 11, with the phase conditions also being optimum for bothcases. As for the oscillation characteristics of an objective lensdriving device of a Comparative Example, having the same structure asthat described above, and in which the supporting member 4 is formed ofberyllium copper (an alloy of beryllium and copper containing not morethan about 3% of beryllium), the resonance frequency (f0) in a directionparallel to the optical axis of the objective lens 2 (FCS) is 31.7 Hz,as shown in FIG. 12, while the resonance frequency (f0) in the planardirection perpendicular to the optical axis of the objective lens 2(TRK) is 27.0 Hz, as shown in FIG. 13.

Thus, with the objective lens driving device of the present invention,employing a stainless material, as the material of the supporting member4, it is possible to achieve oscillation characteristics which areapproximately equivalent to those of the device in which the supportingmember is formed of beryllium copper. The results of our experimentshave indicated that the stainless material used as the material of thesupporting member 4 as in the present invention is also equivalent toberyllium copper as to shock proofness and durability.

The objective lens driving device of the present invention is notlimited to the above-described embodiments but may be constructed suchthat the magnetic circuit unit composed of the yoke and the magnet ismounted on the base member, with the focusing and tracking driving coilsthen being mounted on the lens bobbin. In such case, focusing controland tracking control may be achieved by the interaction between therespective driving coils and the magnetic circuit unit. In this case,the supporting members are not used as feeder lines for supplying thedriving signals to the respective driving coils and are formed ofstainless materials to realize optimum oscillation characteristics.

In the present objective lens driving device, the driving signals aresent to the respective driving coils via a flexible substrateinterconnecting the lens bobbin and the base member. This flexiblesubstrate is formed by a base plate of, for example, polyimide resin,exhibiting flexibility and thermal resistance, and a preset electricallyconductive pattern formed thereon. The respective driving coils areconnected to the electrically conductive pattern on the flexiblesubstrate, and are fed with driving signals via the flexible substrate.

Referring to FIG. 9, the optical pickup device of the present inventionincludes a main body unit 30, on which is mounted the base member 1 ofthe objective lens driving device described above. The base member 1 ismounted on this main body unit 30 via set screws 31 threaded into fourtapped holes 29 provided at its four corners.

Within the main body unit 30 is enclosed a hologram laser device 32,which is made up by substrate 35, carrying a semiconductor laser element33, as a light source, and a photodiode 34, as a light receivingelement, a hologram optical element 36, and a housing 37, having thesubstrate and the hologram optical element enclosed therein. Thehologram optical element 36 separates the light beam radiated from thesemiconductor laser element 33, from the light beam reflected back fromthe optical recording medium, as later explained, and outputs the lightreflected back from the optical recording medium towards the photodiode34.

With this optical pickup device, the light beam radiated from thesemiconductor laser element 33 is transmitted through the hologramoptical element 36 and through an astigmatism correction plate 38 so asto be radiated through an upper through-hole 39 formed in the uppersurface of the main body unit 30. The astigmatism correction plate 38 isa plan-parallel plate, arranged at an angle with respect to the opticalaxis of the light beam output from the semiconductor laser element 33,and corrects the astigmatism proper to the light beam transmittedtherethrough. The light beam radiated from the through-hole 39 of themain body unit 30 is transmitted through the through-hole formed in themid portion of the base member 1 to fall on the objective lens 2.

The light beam incident on the objective lens 2 is illuminated so as tobe converged on a signal recording surface 105 of an optical recordingmedium 104, such as an optical disc. This light beam is modulated as tostrength or direction of polarization, depending on the informationsignals recorded on the signal recording surface 105, so as to bereflected by a reflection layer lined on the signal recording surface105. The light beam reflected back from the reflection layer of theoptical recording medium 104 is re-incident through the objective lens 2to the main body unit 30. The light beam reflected back from the opticalrecording medium 104 falls on the hologram optical element 36 throughthe astigmatism correction plate 36. In this hologram optical element36, the light beam returned from the optical recording medium 104 isdeflected with respect to the optical return path to the semiconductorlaser 36 to fall on the photodiode 34.

The photodiode 34 receives the reflected light from the opticalrecording medium 104, deflected by the hologram optical element 36, tooutput electrical signals corresponding to the state of modulation inthis light beam. It is possible to generate readout signals of theinformation signals, recorded on the optical recording medium 104, basedon the output signal of the photodiode 34. From the output signal of thephotodiode 34, focusing error signals and tracking error signals aregenerated by an error signal generating circuit. Based on the sogenerated focusing error signals and tracking error signals, focusingservo and tracking servo signals are generated by the servo circuit. Theso generated focusing servo and tracking servo signals are sent to thefocusing driving coils 22, 22 and to the tracking driving coils 23, 23,as described above.

In this optical pickup device, the objective lens driving device causesmovement of the objective lens 2, by the respective driving coils 22, 23and the magnetic circuit unit, in the focusing direction parallel to theoptical axis of the objective lens 2 and in the planar trackingdirection perpendicular to this optical axis, such as to cause the lightconverging point of the light beam from the semiconductor laser device32 to follow a recording track on the signal recording surface 105 ofthe optical recording medium 104 by the objective lens 2.

That is, in the present objective lens driving device, the objectivelens 2 is moved in a direction parallel to the optical axis of theobjective lens 2 to cause the light beam radiated from the semiconductorlaser device 33 as the light source to follow the up-and-down movementof the optical recording medium 104 so as to be converged on the signalrecording surface 105 by way of focusing control. In this objective lensdriving device, the objective lens 2 is also moved in a directionperpendicular to a tangential line drawn to a recording track in theplanar direction orthogonal to the optical axis of the objective lens 2to cause the light converging point of the light beam radiated from thesemiconductor laser device 33 as the light source to follow up witheccentricities of the optical recording medium 104 so as to follow therecording track by way of tracking control.

In the above-described focusing control and tracking control, thefocusing error signals corresponding to the distance between the lightbeam converging point and the signal recording surface 105, and thetracking error signals corresponding to the distance between the lightbeam converging point and the recording track, are generated, based onthe output signal from the photodiode 34. The focusing servo signals andthe tracking servo signals are sent as driving signals to the focusingdriving coils 22, 22 and to the tracking driving coils 23, 23, based onthese focusing error signals and tracking error signals.

INDUSTRIAL APPLICABILITY

With the above-described objective lens driving device, according to thepresent invention, in which the power can be supplied to the drivingcoils without employing the supporting members, adapted for movablysupporting the lens bobbin, as feeder lines for the driving coils, itbecomes possible to formed the supporting members of a stainlessmaterial, to enlarge the gamut for the selection of the materials usedfor forming the supporting members and to realize optimum oscillationperformance required of the objective lens driving device.

Since the gamut for the selection of the materials for the supportingmembers, is now wider, it becomes possible to use a stainless material,which is less costly than other metals, to render it possible tomanufacture the apparatus itself inexpensively.

That is, with the present invention, such an objective lens drivingdevice may be provided in which linear supporting members, supportingthe lens bobbin, can be formed easily, the supporting members can bepackaged and transported easily and in which the materials of thesupporting members are readily available and inexpensive.

1. An objective lens driving device comprising: a lens bobbin providedwith an objective lens; a magnet provided on said lens bobbin; a coilunit for causing movement of said lens bobbin along with said magnet ina direction parallel to an optical axis of the objective lens and in aplane perpendicular to the optical axis of the objective lens; astationary unit provided with said coil unit; and an elastic supportingunit formed of a stainless material, provided between said stationaryunit and said lens bobbin for supporting said lens bobbin for movementin a direction parallel to the optical axis of said objective lens andin a plane perpendicular to the optical axis of said objective lens andincluding, a plurality of linear supporting members each having one endthereof mounted to said lens bobbin and having an opposite end mountedto said stationary unit, wherein said elastic supporting unit is formedas a first elastic supporting part and a second elastic supporting part,each said first and second elastic supporting part being respectivelyconstructed having two connecting pieces, each of said two connectingpieces interconnecting ends of two supporting members, of said pluralityof linear supporting members so that said two supporting members extendparallel to each other, and wherein said first and second elasticsupporting parts are arranged parallel to each other on respective sidesof said objective lens, so that said objective lens lies between saidfirst and second elastic supporting parts.
 2. The objective lens drivingdevice according to claim 1 wherein said first and second elasticsupporting parts are punch formed of a stainless sheet material into astainless plate member.
 3. The objective lens driving device accordingto claim 1 wherein said stationary unit has a plurality of grooves forreceiving the opposite ends of said plurality of linear supportingmembers, and wherein a damper is provided in each groove in contact withthe opposite end of the respective linear supporting member.
 4. Theobjective lens driving device according to claim 1 wherein asubstantially rectangular frame-shaped yoke is provided in said lensbobbin, two magnets are provided at a preset distance between two facinginner wall sections of said yoke and wherein said coil unit is providedbetween said magnets.
 5. An objective lens driving device comprising: astationary unit; a lens bobbin provided with an objective lens; a magnetprovided on one of said lens bobbin and the stationary unit; a coil unitprovided on the other of said lens bobbin and the stationary unit andadapted for supporting said lens bobbin for movement in a directionparallel to an optical axis of said objective lens and in a planeperpendicular to the optical axis of said objective lens; and an elasticsupporting unit formed of a stainless material, provided between saidstationary unit and the lens bobbin for supporting said lens bobbin formovement in a direction parallel to the optical axis of said objectivelens and in a plane perpendicular to the optical axis of said objectivelens, including a plurality of linear supporting members each having oneend mounted to said lens bobbin and each having an opposite end mountedto said stationary unit wherein said elastic supporting unit includes afirst elastic supporting part formed of two connecting pieces and asecond elastic supporting part formed of two connecting pieces, each ofsaid two connecting pieces interconnecting ends of two supportingmembers of said plurality of supporting members so that said twosupporting members extend parallel to each other, and wherein said firstand second elastic supporting parts are arranged parallel to each otheron respective sides of said objective lens, so that said objective lenslies between said first and second elastic supporting parts.
 6. Theobjective lens driving device according to claim 5 wherein said firstand second elastic supporting parts are formed of a stainless sheetmaterial punch formed into a stainless plate member.
 7. The objectivelens driving device according to claim 5 wherein said stationary unithas a plurality of grooves for receiving the opposite ends of saidplurality of linear supporting members, and wherein a damper is providedin each groove in contact with the opposite end of the respective linearsupporting member.
 8. An optical pickup device comprising: a lightsource; an objective lens driving device including a lens bobbin,provided with an objective lens for converging a light beam radiatedfrom said light source, a stationary unit having an opening for guidingthe light beam radiated from said light source to said objective lens, amagnet mounted on one of said lens bobbin and said stationary unit, acoil unit provided on the other of said lens bobbin and said stationaryunit and adapted for causing movement of said lens bobbin in a directionparallel to an optical axis of said objective lens and in a planeperpendicular to the optical axis of said objective lens, and an elasticsupporting unit formed of a stainless material provided between saidstationary unit and the lens bobbin for supporting said lens bobbin formovement in a direction parallel to the optical axis of said objectivelens and in a plane perpendicular to the optical axis of said objectivelens; and a photodetector for detecting the light beam incident thereonvia said objective lens, including a plurality of linear supportingmembers each having its one end mounted to said lens bobbin and having arespective opposite end mounted to said stationary unit, wherein saidelastic supporting unit includes a first elastic supporting partconstructed of two connecting pieces and a second elastic supportingpart constructed two connecting pieces, each of said two connectingpieces interconnecting ends of two supporting member of said pluralityof supporting members so that said two supporting members extendparallel to each other, and wherein said first and second elasticsupporting pieces are arranged parallel to each other on respectivesides of said objective lens, so that said objective lens lies betweensaid first and second elastic supporting pieces.
 9. The objective lensdriving device according to claim 8 wherein said first and secondelastic supporting pieces are formed of a stainless sheet material punchformed into a stainless plate member.
 10. The objective lens drivingdevice according to claim 8 wherein said stationary unit has a pluralityof grooves for receiving the opposite ends of said plurality of linearsupporting members, and wherein a damper is provided in each groove incontact with the opposite end of the respective linear supportingmembers.